1. Field of the Invention
The present invention relates to an underground fuel storage tank structure uniquely designed with a built-in sump portion and permanently affixed product piping lines disposed for easy connection to a dispenser. The structure is outfitted with automatic and continuous vacuum extraction of vapor and product that may accumulate within the sump portion. Access is provided to the sump portion. The system is equipped to provide Stage I and Stage II vapor recovery.
2. Related Art
Presently, there are thousands of fuel service stations located across the country. Each year many new service stations are constructed requiring underground storage tanks. In addition, existing service stations are renovated by replacing old fuel storage tanks with new tanks.
Generally, the installation of a fuel storage tank requires the removal of earth creating a deep hole large enough to place the fuel storage tank therein. Underground piping is then connected to the fuel storage tank. The underground piping is provided for filling and venting the fuel storage tank. Other piping is also attached to the fuel storage tank for distribution of its contents to a dispenser.
The fuel storage tank and associated piping are covered with compacted earth or back-fill. A traffic pad made of asphalt or concrete is constructed to support automobiles to be fueled. Finally, a concrete center isle is poured and the dispensers are attached to the underground piping to complete the construction. Upon completion, the piping protrudes through the center isle.
In conventional tank installations, there is typically little or no access to the product piping once construction is complete. Studies have shown that approximately ninety percent of all product leaks and discharges occur through the product piping, even at new installations. Consequently, leak detection devices and double walled product piping are installed during construction to ensure safety. If a leak should occur in the piping, repair can only be accomplished by jack-hammering into the traffic pad and center isle to locate the leak and repair or replace the defective piping. This method of repair can be costly, time consuming and disrupts fuel dispensing service. Underground sumps have been used to contain some of the piping. However, the sump is considered to be an explosive hazard if it is not vented. Furthermore, should a conventional tank need replacement due to a leak or contamination, the cost of replacement becomes substantial since the replacement involves the excavation of the entire old or contaminated tank and the repiping of the venting of the distribution system.